1. Field of the Invention
This invention relates to a process for continuously cooking rice as main meal by steaming and also to an apparatus for carrying the process into practice.
2. Description of the Prior Art
Continuous cookers for producing hard cooked rice for koji making by continuous steaming have been in use by brewers and introduced in varied types. As is well known, the hard cooked rice for koji making is hard steamed rice with a low water content. It is not in the least edible but is intended as a medium for developing koji-mold (e.g., Aspergillus oryzae). Continuous cooking by steaming of rice for direct eating has been called for by central kitchens for feeding service, large messhalls, restaurants, and other installations because it will permit a large volume of rice to be cooked very efficiently. To achieve this end, varied attempts have heretofore been made to modify or improve the existing continuous steam cookers for brewers. However, none of the attempts were fruitful and it has been concluded in the art that edible rice cannot be cooked by continuous steaming alone.
Central kitchens, large restaurants and the like have, therefore, adopted the boiling method in which predetermined quantities of rice and water are placed in a large cooking kettle and heated batchwise. Nevertheless, the batch method has shortcomings of large installation space requirement and limited cooking capacity. If a continuous cooking method is to be employed for cooking a large volume of rice, ancillary devices will be necessary for conveying the cooking kettle, scooping out and loosening the cooked rice, and cleansing the kettle. An additional space for storing the kettle will be needed, too. Thus, the necessity of many varieties of ancillary equipment combines with the installation space and cost requirements to render the continuous method very inefficient.
The specification of Japanese Patent Application Publication No. 20931/1956 discloses a continuous rice steam-cooking apparatus based on the same technical idea as the present invention. The reference cooker operates in the following manner. Washed rice from a hopper is placed, in a layer about 1 cm thick, onto an endless wire screen or slat conveyor outside the cooker body. The washed rice on the conveyor is heated with steam in a primary steaming chamber within the cooker body, and then is further heated in a water bath within a decoction chamber. Heating the washed rice on the conveyor by steaming within the cooker body in the manner described is not practical because of serious drawbacks; heating of the washed rice takes much time, the energy efficiency is very low, and a large volume of steam is wasted. The cooker of the cited invention spreads washed rice in a thin layer about 1 cm thick over the conveyor so that it can be heated as rapidly as possible. This, however, makes the energy efficiency even worse, reduces the cooking capacity, and extends the cooking time. Among other disadvantages is the use of a single endless conveyor that necessitates much driving power, or electric power, consumption for the conveyor operation. In addition, the cited invention does not teach the steam temperature for the cooker and, since no automatic cooker of the contiuous steaming type has been practically used in the art, it is unthinkable that the reference cooker should produce glossy, soft, and full cooked rice pleasant to the palate. For the finishing to a tasty meal the steam temperature for finish steaming is a key point.